The proposed studies will investigate two adaptive mechanisms of vergence eye movements which underlie the development and maintenance of binocular eye alignment. The adaptive mechanisms are changes in tonic innervation to vergence in response to prism and adaptive gain control of interactions between accommodation and convergence. Postnatal development of these two adaptive functions will be examined in normal preschool children over the age range when accommodative esotropia usually appears. Visual and extraretinal stimuli for tonic vergence adaptation will be investigated in normals and strabismic patients with anomalous retinal correspondence who exhibit anomalous fusional movements in response to corrective prism. Comparisons will also be made between the amplitude and duration of adaptive gain changes of accommodative vergence and vergence accommodation in normals and patients with binocular disorders. The results will provide information about adaptive control of vergence, factors underlying the postnatal onset of accomodative esotropia and factors underlying binocular motor disorders such as strabismus which can lead to secondary sensory disorders such as amblyopia.